The following paragraphs contain some discussion, which is illuminated by the innovations disclosed in this application, and any discussion of actual or proposed or possible approaches in this Background section does not imply that those approaches are prior art.
Natural resources such as oil and gas residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing is run in the wellbore. The drilling fluid is then usually circulated downwardly through the interior of the pipe and upwardly through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed. One example of a secondary cementing operation is squeeze cementing whereby a cement slurry is employed to plug and seal off undesirable flow passages in the cement sheath and/or the casing.
These cementing operations generally occur in a wide variety of wellbores ranging, for example, from shallow wells of less than about 1,000 feet to extremely deep wells of greater than about 35,000 feet. The cement composition desirably remains in a pumpable state until it has been placed at its desired location in the wellbore, for example, in the annulus. However, the thickening time of the composition may be unacceptably short to allow it to be pumped to its desired downhole location. As a result, the cement slurry may set in an undesirable location such as inside the casing, which may lead to expensive drill out operations. Set retarders have typically been included in cement compositions to lengthen the thickening times thereof and thereby delay the setting of the compositions until after placement. Some set retarders that are commonly used in cement compositions include lignosulfonates, hydroxycarboxy acids, phosphonic acid derivatives, synthetic polymers (e.g., copolymers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS)), borate salts, and combinations thereof.
Often the temperatures in a wellbore increase from the top down to the bottom of the wellbore. Unfortunately, increasing the temperature of a cement composition results in a decrease in the thickening time of the composition. Thus, in wellbores having bottom hole circulating temperatures (BHCT) above about 350° F., conventional set retarders commonly fail to sufficiently lengthen the thickening times of cement compositions to allow those compositions to be pumped to their desired downhole locations. Therefore, the use of such set retarders limits the depths and associated temperatures at which wellbores may be drilled and isolated with cement compositions.
To overcome such limitations, traditional set retarders have been supplemented with ethylenediamine tetra acetic acid (EDTA) or its sodium (Na) salt to intensify their retardation effect on the setting of cement compositions at higher temperatures. The combination of the traditional set retarders with the EDTA or its Na salt typically provides for desirable levels of set retardation in cement compositions subjected to BHCT's as high as 525° F. or even higher. However, EDTA and its Na salt suffer from the drawback of being toxic and having a relatively low biodegradability, i.e., its susceptibility to breakdown by microorganisms. As such, their use is often limited to low concentrations or even restricted entirely in places such as the United Kingdom and the North Sea where strict environmental regulations apply. Further, EDTA and its Na salt are costly to produce. It is therefore desirable to develop a less expensive set retarder composition that is non-toxic and exhibits a relatively high biodegradability.
Additional information relating to conventional set retarders may be found in U.S. patent application Ser. Nos. 10/963,036 and 10/963,035, filed on Oct. 11, 2004, each of which is incorporated herein by reference.
Some teachings and advantages found in the present application are summarized briefly below. However, note that the present application may disclose multiple embodiments, and not all of the statements in this section necessarily relate to all of those embodiments. Moreover, none of these statements limit the claims in any way.
According to various embodiments, methods of retarding the setting of a cement composition comprise including one or more secondary amines substituted with a carboxyl group or salts thereof (e.g., 3-hydroxy N,N′-iminodisuccinic acid) in the cement composition. As used herein, “secondary amines substituted with a carboxyl group” not only refers to the amines themselves but also refers to copolymers thereof, terpolymers thereof, block polymers thereof, or any combination thereof. The inclusion of such materials in cement compositions may be highly beneficial. In wellbores having bottom hole circulating temperatures (BHCT's) of less than or equal to about 250° F., the use of the secondary amine as the set retarder ensures that the thickening time of the cement composition is sufficient to allow the cement composition to be pumped to its desired downhole location. Further, the secondary amine may be used in combination with conventional set retarders to enhance the ability of those retarders to increase the thickening time of the cement composition at higher BHCT's, e.g., from about 250° F. to about 525° F.
In addition, such secondary amines substituted with a carboxyl group or salts thereof exhibit relatively low levels of toxicity and relatively high biodegradability percentages (e.g., greater than 60%). Thus, they may be employed in cement compositions without being concerned that they could harm the environment. Advantageously, they can be used in places that have strict requirements on the levels of toxicity and biodegradability. In addition, the secondary amines may be produced at relatively low cost. As such, their inclusion in cement compositions would not prohibitively raise the cost of producing such compositions.